Conventionally, many patch antenna (microstrip antenna) devices are used as antenna devices used for radar etc, for example, as disclosed in JP1993-206729(A).
The patch antenna device typically includes a dielectric substrate, a patch made of a thin-film conductor formed on one side of the dielectric substrate, a ground formed on the other side of the dielectric substrate, and a feeder line made of a thin-film conductor that is formed on the one side of the dielectric substrate and is coupled to the one end of the patch. Such a patch antenna device radiates an electromagnetic wave from the patch in a direction perpendicular to the substrate when electric power is supplied to the patch through the feeder line. However, such a patch antenna device radiates from the feeder line, that is located on the dielectric substrate as well as the patch, electromagnetic waves produced by current flowing through the feeder line (hereinafter, referred to as “disused radiations”) in a direction perpendicular to the substrate. Therefore, because the electromagnetic waves from the patch and the disused radiations are radiated to the same direction, the electromagnetic waves radiated from the patch will be influenced by the disused radiations. As a result, it may be difficult to radiate electromagnetic waves having designed characteristics.